1. Technical Field
The invention relates to non-pneumatic tires for use with tracked vehicles.
2. Background Art
Tracked vehicles have applications in military use, heavy commercial use, and others where the vehicle may be travelling over uneven terrain, carrying a heavy load, or the like. The vehicles have a track which interfaces with the ground to support or propel the vehicle. Wheels are located within the track to drive or support it. Some of the wheels are connected to the drivetrain of the vehicle. A tire is placed over the rim of the wheels to interface with the track to improve ride quality characteristics. The tires are typically made from a natural or synthetic rubber and are solid, or non-pneumatic.
Typical failure modes of these rubber tires are blow-out and heat checking from high operating temperatures, cutting and chunking from sharp debris, and bonding failure at the rubber-wheel interface. Failure of the elastomer rubber tire on the road wheel may account for more than ninety-five percent of all road wheel failures. For temperature failures, the primary source of heat generation is hysteretic heating from the rubber, with vehicle speed and ambient temperatures as strong contributors. The higher the operating speed of the vehicle, the greater the number of hysteretic cycles the elastomer goes through, and consequently the higher the operating temperature. The thickness of the elastomer has a major affect on the hysteretic heating. Typically a thicker tire and a lower modulus generate greater hysteretic heating, but provide better damping for reduced vehicle vibrations. As a result the compound is blended for a compromise in these design features.
For cutting and chunking, sharp pointed debris material indents the elastomer. Once the elastomer tensile forces at the tip of the debris exceed the tensile strength of the elastomer, a crack initiates and then begins to propagate. Two usual methods to prevent crack initiation include using a higher modulus elastomer or a thicker tire. Unfortunately, the tensile strength of elastomer decreases drastically with higher operating temperatures over 175 F or 200 F. The higher temperatures promote crack initiation by weakening the tire.
Currently, tire improvements are being sought through use of higher temperature formulations, polyurethane or poly urea, or optimized width and thickness of the rubber.
The cutting and chunking characteristics may be improved with polyurethane, but drawbacks include a lower operating temperature threshold, a harder ride with increased vibrations, additional cost, and greater susceptibility to contaminants and humidity during adhesion molding.